The present invention relates generally to a heat reclaiming method and apparatus, and more particularly to a method and apparatus for reclaiming the normally wasted heat rejected by the refrigerant of a refrigeration circuit by transferring such heat to a hot water heat sink.
Refrigeration systems generally comprise a compressor, condenser, and expansion device, and an evaporator connected by appropriate refrigerant lines to form a refrigeration circuit. Refrigerant vapor is compressed by the compressor and fed to the condenser where the refrigerant rejects heat to a cooling medium and condenses. The condensed refrigerant then flows through the expansion device, reducing the pressure and temperature of the refrigerant. From the expansion device, the refrigerant passes into the evaporator, absorbs heat from a medium which is thereby cooled, and vaporizes. Vaporous refrigerant is then drawn back into the compressor, completing the circuit.
Such refrigeration circuits are frequently employed to cool a fluid such as air which is circulated through various rooms or areas of a building to cool these areas. Often the refrigerant of such a circuit rejects a relatively large amount of heat at the condensor of the circuit. This rejected heat is commonly dissipated to the atmosphere, either directly or via a cooling fluid that circulates between the condenser and a cooling tower. Over a period of time, the rejected heat represents a substantial waste of energy, and recently much attention has been directed to reclaiming or recovering this heat.
One general approach to reclaiming this heat has been to position a heat reclaiming heat exchanger between the compressor and condenser of the refrigeration circuit wherein the hot, compressed refrigerant vapor discharge from the compressor flows through the added heat exchanger. Water is circulated through the heat reclaiming heat exchanger in heat transfer relation with the vapor passing therethrough and heat is transferred from the vapor to the water, heating the water and cooling the vapor. The heated water is conducted to a storage tank where the water may be stored for later use, and the cooled vapor is directed to the condenser of the refrigeration circuit where the vapor is further cooled and condensed.
Numerous patents have been granted to systems for utilization and recovery of this waste heat.
U.S. Pat. No. 4,254,630 is directed to a heat reclaiming method and apparatus for use in a vapor compression refrigeration circuit. The apparatus comprises a heat exchanger connected to a compressor and a condenser of the refrigeration circuit for receiving refrigerant vapor from the compressor and discharging the refrigerant to the condenser wherein the refrigerant vapors pass in heat transfer relation with heat transfer fluid to heat the fluid and cool the vapors. The heat exchanger is further connected to a source of the heat transfer fluid for receiving fluid therefrom and still further connected to the heat storage facility for discharging the heat transfer fluid thereto, The heat reclaiming apparatus further comprises a valve for regulating the flow of heat transfer fluid to the heat exchanger; and a control for controlling the valve to decrease the quantity of heat transfer fluid flowing to the heat exchanger when a temperature of the heat transfer fluid discharged therefrom falls below a predetermined value.
U.S. Pat. No. 4,251,996 is directed to a heat reclaiming method and apparatus which comprises a heat reclaiming condenser connected to the refrigeration circuit for receiving refrigerant vapor therefrom and discharging condensed refrigerant thereto further connected to a source of heat transfer fluid for receiving fluid therefrom still further connected to the heat storage facility for discharging the heat transfer fluid thereto wherein refrigerant vapor passes in heat transfer relation with the heat transfer fluid to heat the fluid and condense the refrigerant vapors. A valve is provided for regulating the flow of heat transfer fluid to the heat reclaiming condenser and a valve control for controlling the valve to decrease the quantity of heat transfer fluid flowing to the heat reclaiming condenser when the condensed refrigerant reaches a predetermined level.
U.S. Pat. No. 4,238,931 is directed to a waste heat recovery system controller for use in a waste heat recovery subsystem utilizing a heat exchanger, such as a refrigeration system having a heat exchanger for extracting and recovering heat energy from the superheated refrigerant by means of a transfer fluid. A combination of three interactive control systems is provided for control of the flow of heat transfer fluid through the heat exchanger. A first sensor means determines when the waste heat temperature is sufficiently high and controls a pump to obtain a circulation of the fluid when such temperature exceeds a preselected value. A second sensor monitors the temperature of the heat transfer fluid and stop circulation of the fluid when such temperature exceeds a preselected safe upper limit. A third sensor monitors the transfer fluid temperature at the outlet of the heat exchanger and controls the rate of flow of fluid in a manner proportional to such temperature.
U.S. Pat. No. 4,281,519 is directed to a refrigeration circuit heat reclaiming method and apparatus wherein heat energy is exchanged between a refrigeration circuit and a hot water system. A restricted flow bypass line is used in conjunction with a pump continuously operated with a compressor of the refrigeration system such that a continual restrictive flow of water bypasses the water or the heat exchanger when temperature conditions are such that water is not flowing through the heat exchanger.
U.S. Pat. No. 4,199,955 is directed to heat extraction or reclamation apparatus for a refrigerating and air conditioning system. This system is adapted to recover otherwise rejected heat from the refrigerant gas flowing through air conditioning and refrigeration systems and includes a counterflow heat exchanger for transferring heat to a medium such as water which heat exchanger is installed upstream of the conventional condenser. The heat extraction system has a pump for circulating water or other medium to be heated, located on one side of the heat exchanger. Hot refrigerant gas from the compressor is circulated through the other side of the heat exchanger. The pump flow rate in the heat transfer area between the refrigerant gas and the water are chosen to insure that the refrigerant gas outlet quality remains within limits which insures flow continuity and operation. Refrigerant gas leaving the system will contain some liquid in the form of droplets. The water temperature is maintained within limits by stopping the pump when the inlet pressure change pressure to water temperature reaches the predetermined maximum value.
U.S. Pat. No. 3,922,876 is directed to an energy conservation unit for utilizing waste heat, from an air conditioner for refrigeration systems, to heat water. The system includes a heat exchanger coupled in the output of the compressor of the air conditioner for a refrigeration system and to a water reservoir for effecting heat transfer. A pump is interposed between the water reservoir and the heat exchanger for circulating the water. A temperature sensor thermally coupled to the water and electrically coupled to the pump is provided for rendering the pump inoperative when the temperature of the water in the reservoir is at or above a preselected temperature. A temperature operated valve is interposed between heat exchanger and the reservoir such that only water heated to a predetermined temperature is delivered to the reservoir.
U.S. Pat. No. 2,668,420 is directed to a combination water heating and room cooling system and method employing heat pumps providing an improved control network for a combination heating and cooling system so that a system may be readily set primarily for heating water or primarily for both heating and cooling the room.
Thus, in the typical vapor compression refrigeration system, various components such as the compressor, condenser, evaporator and expansion device are arranged to transfer heat energy between the fluid in heat exchange relation with the evaporator and fluid in heat exchange relation with the condenser. It is also known in conjunction with such refrigeration systems to utilize a desuperheater for removing superheat energy from gaseous refrigerant prior to circulating said refrigerant to the condenser.
In a conventional building installation, a hot water heater is provided to supply heated water to an enclosure.
Many hot water heaters have a cold water inlet connected to an inlet extension pipe and a hot water outlet extending through the top of a hot water tank. Often, an inlet extension pipe is connected to the cold water inlet such that the incoming water is directed to the bottom portion of the tank. In hot water tanks, water is heated at the bottom of the tank and rises such that a stratified tank with relatively warm water at the top and cool at the bottom is provided. When demand is made for hot water, water is discharged from the top of the tank at its warmest temperature and cold water is supplied through the inlet to the bottom portion of the tank.
It is known to combine a refrigeration system and hot water heating system such that the superheat of the refrigerant may be rejected to water to be heated such that this heat energy may be utilized to provide hot water.
In air conditioning systems when cooling is required, heat energy is transferred from the enclosure and discharged to the ambient or some other heat sink. This heat is often wasted. With combination systems as disclosed herein, it can be seen that this heat energy which is unwanted in the enclosure may be utilized to supply heat energy to water to provide heat and water for various uses. This heated water may be used for bathing, cleaning, cooking or other uses in a home or business. Commercial applications include restaurants, supermarkets, process utilization and any other application wherein wasted energy or excess energy from a refrigeration system may be utilized to provide some or all of the hot water heating needs.
In addition to refrigeration systems providing excess heat for heating water during the cooling season, certain refrigeration circuits are capable of reversing the cycle of operation for providing heat energy to the enclosure during the heating season. If it is desirable, some of the heat provided during the heating season may also be utilized to supply hot water through a hot water heater refrigerant desuperheater.
The energy situation and related economic instability are serious long-term problems. The refrigerant cycle can be employed to conserve energy and save money by heating hot water with the heat available in the superheater refrigerant of the refrigerant cycle. Where the refrigerant cycle is used for cooling, service such as air conditioning and food preservation, heat available to heat hot water is 100% waste heat, and it can be used beneficially to conserve non-renewable energy and greatly reduce water heating costs. Where the refrigeration cycle is used in the form of the heat pump, the same holds true for cooling cycle operation. With heating cycle operation, the available portion of the heat brought in through the evaporator and the heat equivalent of compressor work are available to heat hot water. The heat brought into the evaporator in the heat pump cycle, is generally from renewable sources such as ambient air, low temperature geothermal, and solar energy, converted heat or waste heat. The heat equivalent of compressor work is non-renewable energy for most refrigerant cycles such as electric power or natural gas. Photovoltaic or solar powered Rankine cycle driven heat pumps are examples where the heat equivalent of compressor work would be renewable energy.
In the specific embodiment disclosed, a pump is used to circulate water from the hot water tank through the heat exchanger and back to the hot water tank when the compressor of the refrigeration circuit is energized. A temperature sensing device is located to sense the temperature of the water in the hot water tank and when the temperature of the water therein falls below a predetermined value, the circulation pump is actuated to pump water through the heat exchanger back to the hot water tank for storage. When the refrigeration compressor operates in response to load requirements, cool water from the lower portion of the hot water storage tank is circulated by hot water circulator pump through the double-walled superheat refrigerant to the water heat exchanger. The water is heated in the heat exchanger and is pumped back to the upper portion of the hot water storage tank. The hot water stays in the upper part of the storage tank because of its lower density than the cold water. Preferably, the hot water storage tank is insulated to reduce heat loss by conduction and radiation from the tank surface. When hot water is withdrawn from the storage tank, it is drawn from the top of the tank where the hottest water resides. The cold water flows into the tank horizontally and rises uniformly in the tank as hot water is withdrawn from the top.
When the refrigerant compressor is not operating, a standby heater operates to maintain a desired water temperature in the upper 20%-30% of the tank. The standby heater is operated automatically by a thermostatically controlled switch which actuates upon the storage tank water temperature falling below a predetermined temperature. In like manner, the switch de-activates when the water temperature rises to the desired level. A two-position three-way automatic drain valve is positioned between the outlet of the pump and the inlet of the heat exchanger and a check valve is positioned between the outlet of the heat exchanger and the inlet to the hot water storage tank. An air bottle or other source of air is connected through a valve to a point between the outlet of the heat exchanger and the inlet to the check valve.
When the water temperature in the hot water storage reaches a predetermined upper temperature limit, the limit switch positioned in the upper part of the hot water tank actuates the two-position three-way automatic valve to cause closing of the valve to the outlet of the pump and opening a passage between the heat exchanger and an external drain. The draining operation reduces the water pressure in the heat exchanger and due to the higher water pressure in the storage tank, the check valve will close isolating the water side of the superheated refrigerant to heat exchanger from the water directed to the hot water storage tank. The compressed air in the air bottle is introduced into the line between the check valve and the heat exchanger purging the water in the heat exchanger through the external drain to prevent the generation of steam and overheated water within the refrigerant cycles desuperheating hot water heater heat exchanger.
When the water temperature in the hot water storage tank falls below the setting of the high temperature switch, the two-position three-way valve returns to normal operation for conducting of water from the pump to the heat exchanger. The water pumped through the heat exchanger compresses the trapped air back into the air bottle and equalizes the water pressure on both sides of the check valve which opens.
The prior art devices disclose operating the pump continuously with a compressor, the use of a solenoid valve or other valve to control the flow of water through the heat exchanger and the use of a bypass line to circulate the flow of water around the heat exchanger when the water temperature exceeds a safe limit. None of the prior art disclosures discloses the combination of a temperature sensitive relief valve positioned in the hot water storage tank to heat exchanger circuit which coacts with a check valve and air supply between the heat exchanger and the hot water tank to purge the heat exchanger of water when a predetermined high temperature limit is detected in the hot water storage tank.